UNITED NATIONS — With the United States and its allies pressing President Bashar al-Assad to step down, the Arab League last week issued a detailed plan for a political transition in Syria. The plan was welcomed by the Obama administration, and Arab leaders quickly said they would refer it to the United Nations.

And a day later, Russia had its say: Not a chance.

“This is an effort from the Arab League, if I understand correctly, to sort of already put a precooked solution on the table,” said Vitaly I. Churkin, Moscow’s envoy to the United Nations. “I understand that the attitude of Damascus to that has been negative.”

The response doomed any hope of a quick resolution at the United Nations to bring greater pressure to bear on the Syrian government, but it also fell into a familiar pattern by which Moscow has shown a growing willingness to challenge the United States and its European partners on a range of issues.

In recent weeks, Moscow has sought U.N. scrutiny of possible crimes by NATO during its air campaign in Libya, and even called for investigations into organ sales in Kosovo, a close ally of the West. Most notably, Moscow has obstructed any effort to increase pressure on Iran.